1. Field of the Invention
The invention relates to a process for preparing bis(amidocarboxylic acids) which are key intermediates in the synthesis of bis(amidoperoxycarboxylic acid) bleaches.
2. Related Art
Peroxyacids have long been known for their excellent fabric bleaching activity. More recently, amido peroxycarboxylic acids have been identified as particularly desirable because of their good stability in detergent compositions.
U.S. Pat. No 4,634,551 (Burns et al) and U.S. Pat. No. 4,686,063 (Burns) describe peroxyacids having polar amide links along a hydrophobic backbone. All of the reported substances are monoperoxycarboxylic acids. U.S. Pat. No. 5,061,807 (Gethoffer et al) and U.S. Pat. No. 5,132,431 (Fuchs et al) describe a series of imido peroxyacids, chief among which is N-phthaloylaminoperoxycaproic acid (PAP). See also the related technology in EP 0 347 724 (Ausimont).
Bis(amidoperoxy acids) have been disclosed in WO 90/14336 (Interox) which especially describes N,N'-terephthaloyl-di(6-aminoperoxycaproic acid), known as TPCAP. The exceptional stability of TPCAP, and related compounds, have occasioned the need for an improved synthesis. Especially necessary is a route to the intermediate N,N'-terephthaloyl-di(6-aminocaproic acid) known as TOCAP.
The literature has described various syntheses for TOCAP and related compounds. German Patent 949,568 (Kruckenberg) describes the reaction of caprolactam with various acyl halides including adipoyl dichloride in the presence of sodium hydroxide. Once sodium 6-aminocaproate has formed, the reactor is charged with a first portion acyl halide, sodium hydroxide and then a final portion acyl halide. Example 1 best details this process. Synthesis of TOCAP is reported by Zinner et al in J. Prakt. Chem. 17, 147-153 (1962). The procedure requires the addition of all the sodium hydroxide to be charged to the reaction vessel at the beginning of the synthesis. The reported yield is 70% of theory. Plate-like crystals are recovered through recrystallization from dimethyl formamide/water (2:5).
The problem with the aforementioned synthetic routes is that the yields are insufficiently high for commercial purposes. Secondly, these syntheses result in substantial amounts of undesirable by-products, especially the monoamide addition by-product. These by-products can lead to thermal instability and impact sensitivity in any eventual peracid formed therefrom.
Accordingly, it is an object of the present invention to provide an improved synthesis of bis(amidocarboxylic acids).
A more specific object of the present invention is to provide a route to bis(amidocarboxylic acids) that achieves high yields.
A further specific object of the present invention is to provide a route to bis(amidocarboxylic acid) in which undesirable by-products are minimized.
A still further object of the present invention is to provide a route to bis(amidocarboxylic acid) through an environmentally friendly procedure wherein product cleanly and with minimal workup separates from the reaction medium.
These and other objects of the present invention will become more readily apparent through consideration of the following summary, detailed description and examples.